Contents

Abstract

Cocoa is the main commodity crop of Ghana and is financially important
for the livelihood of many rural communities. The relatively recent
arrival of the more aggressive black pod pathogen Phytophthora
megakarya and its continued progress westwards threatens the cocoa
farming communities. In a wider context its recent arrival in Ivory
Coast, currently the worlds largest producer of cocoa, has implications
for West Africa and global cocoa production. In Ghana it has already led
to some farmers abandoning cocoa in Ashanti and to a lesser extent in
the Western regions.

Studies undertaken by scientists at CRIG have shown that although
cultural practices are effective for the control of P.palmivora they
are inadequate for the control of P.megakarya. The supplementation of
cultural practices with chemical application is essential to reduce the
impact of P.megakarya. Recently CRIG scientists reported that
fungicide adoption is on the increase in P.megakarya infected
districts. Current recommendation is for the application of
copper/metalaxyl formulations. The Ghanaian government has initiated a
national spraying programme, centrally funded. However, in the long-term
an alternative to the current copper based products is required. The
application of these chemicals is expensive and often incorrectly
applied by farmers, in addition the accumulation of these compounds in
the environment could have long-term effects on soil biology and
productivity of the cocoa agro-ecosystem. Phosphonic acid has been shown
to be an effective, economically viable and environmentally safer
alternative control agent of Phytophthora spp. in cocoa and other crop
systems around the world.

Results are presented of field trials carried out over 3 years to assess
the potential of phosphonic acid applied as stem injection, pod spray
and paint in comparison to spray application of copper compounds. Six
spray applications of the copper compounds and phosphonic acid were made
over the season, in accordance with current recommendations for copper
fungicides. Stem injection of phosphonic acid was applied once in a
growing season. Comparative studies were implemented in Bechem, where
P.megakarya is present and at Tafo where only P.palmivora is
present.

Application of phosphonic acid as a one-off stem injection was shown to
reduce the incidence of P.megakarya. Control achieved was similar to
that achieved with the current recommended control regime. Implication
of these results for the implementation of stem injection of Phosphonic
acid as an effective, economically viable and environmentally safe
alternative to copper fungicides is discussed.

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